Wavelength Division Multiplexing (WDM) is a currently common optical layer networking technology, and it is easy to realize a transmission capacity of Gbit/s or even Tbit/s by multiplexing different wavelengths into an optical fiber for transmission. A Reconfigurable Optical Add/Drop Multiplexer (ROADM), which is a core optical switching device in a WDM network, can configure any wavelength at any port. A wavelength selective switch (WSS) is a new-generation technology used to realize a dynamic ROADM, and has a function of selecting and outputting a particular wavelength from input wavelengths.
A WSS based on Liquid Crystal on Silicon (LCOS) can realize flexible tuning of a channel center frequency and a channel bandwidth, and such bandwidth-tunable WSS can meet requirements of operators for a ROADM with a flexible bandwidth in a next-generation network. LCOS is a spatial light modulation device, which controls a phase of each liquid crystal cell through a voltage to adjust the wavefront of an incident light, so that a direction of the incident light is deflected. Generally, a conventional LCOS uses a nematic phase liquid crystal material. Since the nematic phase liquid crystal has optical anisotropy, it presents different refractive indices for light components of different polarization types when the incident light undergoes a phase modulation. Thus, the LCOS has polarization dependence. In order to eliminate the polarization dependence, a depolarization device must be disposed in the LCOS-based WSS. This will increase complexity of an optical path, bring an insertion loss (about 0.5 dB), and increase a cost.
Therefore, there is a need for a new wavelength selective switch, which can realize wavelength selection through a simple structure and meanwhile reduce the insertion loss brought by the wavelength selective switch.